To define the recommended dose for phase II trials of irinotecan combined with cisplatin and etoposide in chemonaive patients with stage IV disease, 56 patients (11 having SCLC and 45 NSCLC) received cisplatin 25 mg m−2 weekly for 9 weeks, etoposide 60 mg m−2 for 3 days on weeks 1, 3, 5, 7 and 9, and irinotecan 20–100 mg m−2 (levels 1–8) on weeks 2, 4, 6 and 8, together with a prophylactical granulocyte colony-stimulating factor support (50 μg m−2 on days 4–7 on weeks 1, 3, 5, 7 and 9, and on days 2–7 on weeks 2, 4, 6 and 8). The gene discussed is CSF3; the disease is small cell lung carcinoma.